DESCRIPTION: Lesions of the posterior parietal cortex (PPC) in humans and monkeys produce deficits in visual attention, spatial perception, and the ability to make accurate movements. These deficits are the result of losing the cortical pathway which enables visual information to be transformed into action. This proposal will examine how this transformation is accomplished by recording the activity of neurons in the PPC of monkeys while they perform various visual-motor tasks. The proposal will focus on whether a component in PPC is already coding movement intentions, whether these intentions are coded in the motor coordinates of the movement being planned, and how the different sensory signals that converge on PPC are transformed into various spatial coordinate frames. The role of gain fields (the modulations of sensory signals by eye, head and limb position) in transforming between coordinate frames will be examined. The first specific aim will examine movement intention and will determine if cells in area LIP are specifically engaged in saccade tasks, and if cortical areas around LIP are specifically engaged in reach tasks. The second specific aim will determine if reach-related areas are coding visually derived signals in limb coordinates. Such a finding would indicate that visual signals have been transformed into motor coordinates for the purpose of moving the limbs. The third specific aim will examine how head position signals are combined with eye position and visual (retinal position) signals to code the spatial locations of objects. It will be determined if vestibular signals, which convey information about the location of the head in the world, affect the visual response of PPC neurons; these vestibular gain fields could potentially encode locations in world-centered coordinates. Likewise it will be determined if neck proprioceptive or efference copy signals, conveying the orientation of the head on the body, modulate visual responsiveness and potentially encode locations in body-centered coordinates. Finally the role of optical flow and visual landmark cues in coding the locations of visual stimuli in world-centered coordinates will be examined. The fourth specific aim will be to determine how visual and auditory signals are combined in PPC to code spatial locations independent of the modality of the stimulus. These experiments, particularly the third and fourth aims, are designed to answer the long standing question of how different modalities are combined into a common framework in parietal association cortex. Overall these experiments will significantly further our understanding of how perceptions are transformed into actions.